Is an empty while loop considered bad practice?

Question

I am to download data from the server, with a maximum of 3 attempts if the download fails.

public class DownloadFile {

    private boolean isSuccessful;

    public DownloadFile() {
        int attempt = 0;

        while(!isSuccessful && (attempt++ < 3)) {
            DownloadFileThread.start();
            while (DownloadFileThread.isAlive());
        }
    }

    private Thread DownloadFileThread = new Thread() {
        public void run() {
            try {
                // download file from server

                isSuccessful = true;
            } catch (Exception e) {
                isSuccessful = false;
            }
        }
    }

}

As you can see in the above example, I have an empty while loop in (what would be) line 10 to force guarantee isSuccessful is assignment a value based on the outcome of the DownloadFileThread before checking the condition in the while loop again.

Is it considered bad practice to do such a thing? Is there better approach or a correct way to do this?

While the above code does produce a valid result, I am not exactly proud of the code I have written...

Answer 1

Yes, in this case it is a bad practice, because Java offers better mechanisms to wait for completion of a thread: Thread.join(), or consider using more modern features like CompletableFuture or an ExecutorService that allows you to wait for a task to complete.

Using an empty loop to wait will consume a lot of CPU power unnecessarily, which might mean other tasks on your system will perform slower than they could otherwise.

Answer 2

Not necessarily, but in this case this is a busy wait which is bad practice especially in multi-threaded programs. It keeps the CPU busy and in your case interferes with DownloadFileThread.